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    <title>Document</title>
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<script>
    /*
        1、数字类型转换为字符串类型，值扔为数
        字类型时的值，但是类型变为字符串雷兴国
        可以使用 + ""来进行隐式的转换
        2、布尔转换成字符串就是true和false
        3、String（）进行类型的强制转换
    */
    var num = 12345;
    var notnum = NaN;
    var str1 = num +"";
    var str2 = notnum + "";
    document.write(str1 + "<br>", str2 + "<br>");

    var u1 = undefined;
    var n1 = null;
    var str5 = String(u1);
    var str6 = String(n1);
    document.write(str5 + "<br/>", str6 + "<br>");


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